The patellofemoral joint of the knee is an articulating joint between the patella and the femur. More specifically, this joint consists of an articular surface on the posterior of the patella and a corresponding articular surface on the anterior distal portion of the femur, also termed the trochlear groove. The posterior of the patella is contoured as a ridge, while the trochlea is contoured as a groove that is dimensioned to receive the patellar ridge in a complementary manner. Proper dynamic function of the patellofemoral joint requires that the patellar ridge accurately track the underlying trochlear groove when the knee is moved through flexion or extension.
Joint disorders nevertheless arise with varying severity, pain and dysfunction. Some less severe, albeit still painful, disorders involve minimal or no errors in patellar tracking of the trochlear groove. Other more serious disorders are characterized by patellar subluxation, i.e., transient displacement, or dislocation, i.e., permanent displacement, of the patella from the trochlear groove.
Most frequently, such tracking errors occur in the lateral direction and therefore require corrective medial traction. During functional movement of the knee joint, that is—typically from 0° to 60° of knee flexion, lateral tracking can occur due to injury, overuse, or changes inherent to adolescent growth, which in each of these cases causes pain and dysfunction. When the patella is seated in the trochlear groove at a range greater than about 60° of knee flexion, there is very little movement of the patella outside of the trochlear groove. Between about 0° and 40° of knee flexion, and especially about 20° to 40°, however, there is a propensity for the patella to track laterally as the knee flexes. As a result, effective medial traction forces must be applied in conjunction with exercise to direct the patella for improved tracking.
Rehabilitation of the weakened joint is therefore limited to the extent that true medial traction is absent, or ineffectively applied. While some devices may stabilize the patella, they fail to provide consistent, continuous traction force, and therefore fail to affect proper patellar tracking. It is important, moreover, to provide medial traction (and not mere stabilization) throughout a full range of knee flexion and extension motion.
In addition, biomechanical forces typically bias the patella laterally when the knee is load bearing. During knee extension, the quadriceps contract to exert a lever force about the patellofemoral joint, whereby the patella is pulled up along the trochlear groove. As the patella moves up the trochlear groove, the trochlear groove narrows, thereby forcing the patella to project more outwardly. Nearly simultaneous application of load bearing pressure may result in either momentary or permanent lateral displacement of the patella such that medial traction must be used to correct or prevent the prevailing lateral subluxation or dislocation.
As the quadriceps contract, they apply a lever force to the patellofemoral joint that is, more or less, directly related to the overall patellofemoral joint stress. Pain associated with such stress increases in relation to the amount of overall stress. Accordingly, as the quadriceps contract more powerfully, such as while going up stairs or doing squats, overall stress and associated pain increases.
However, patellofemoral joint stress at any given contact area decreases as the overall patellofemoral joint stress is distributed about a greater patellofemoral contact surface area. Pain associated with such stress decreases in inverse relation to the amount of patella-to-femur contact surface area. Thus, patellofemoral pain is not only directly related to the overall joint force applied between the patella and the femur; it is inversely related to the amount of patellofemoral contact surface area. Rehabilitation of the weakened joint through quadriceps contraction is therefore limited by the pain associated with both overall patellofemoral joint stress and a minimal patellofemoral contact surface area.
Because subluxation frequently occurs even early on in the extensor motion, it is moreover important to account for the damage and pain caused by both overall joint stress and a minimal patellofemoral contact surface area, throughout a full range of knee flexion and extension motion.
Prior attempts to provide patellofemoral support fail to provide continuous medial tracking or account for patellofemoral contact surface area as a factor in joint stress. For example, U.S. Pat. No. 6,287,269 B1, entitled “Dynamic Orthesis Device for the Conservative Treatment of Patellofemoral Instability of the Knee”, discloses a support element that provides medial tracking of the patella. Continued medial traction is absent, however, and it does not account for damage and pain caused by minimal patellofemoral contact surface area, however.
U.S. Pat. Nos. 6,077,242 and 6,080,124, respectively entitled “Patella Strap” and “Patella Strap Method”, disclose a strap that directs either superior or inferior, i.e., downward or upward, pressure on a patella. Continued medial traction is absent, however, and it does not account for damage and pain caused by a minimal patellofemoral contact surface area, or provide medial tracking of the patella.
U.S. Pat. No. 6,592,539 B1, entitled “Orthotic or Prosthetic Sleeve Formed of Elasticized Fabric Sections Having Different Elastic Stiffness”, discloses a compression sleeve having a section that fits over the entire knee and includes unidirectional stretchable fabric that stretches along the sleeve's axis. It does not, however, account for damage and pain caused by a minimal patellofemoral contact surface area, or provide medial tracking of the patella.
U.S. Pat. No. 4,607,628, entitled “Patella Support Brace”, discloses a patella pad that exerts a medial and distal pressure on the patella during knee extension. Continued medial traction is absent, however, and it does not account for damage and pain caused by minimal patellofemoral contact surface area.
U.S. Pat. No. 6,551,264 B1, entitled “Orthosis for Dynamically Stabilizing the Patello-femoral Joint”, discloses a knee orthosis having a patellar tracking guide that tensions as the knee extends. It does not, however, account for damage and pain caused by a minimal patellofemoral contact surface area, or provide medial tracking throughout a full range of knee flexion and extension motion.
Hence, the prior art fails to provide a knee brace that provides medial traction and that accounts for pain caused by a minimal patellofemoral contact surface area throughout a full range of flexion and extension motion.